The moving wall for sure. Of course the first time I played FFIV(many, many, moons ago), I wasn't reading what the battle message was saying when I fought the Mist Dragon at the beginning of the game, so I couldn't figure out why I kept getting obliterated when it turned into mist(I thought that it turned into mist for the rest of the battle after you take off so many hit points off) and I kept on hammering it. Finally I figured it out after I started reading the battle messages(four or five tries later). Curse the short attention span of being a kid!.